This invention relates to linear detector circuits and more particularly to solid state diode detector circuits including means for compensating the nonlinearities of the diodes with variations in their operating temperature and signal input level.
In demanding applications such as video detectors for high performance radar systems, linearity of detector operation must be maximized over a broad range of operating temperature and input signal levels. For example, in some applications of this kind specifications may call for linearity of detector operation within a tolerance of half a decibel over a signal input range of thirty or forty decibels and over a temperature range of perhaps fifty degrees celsius. Efforts have previously been made to improve linearity of diode detectors employing a number of expedients, such as the provision of a prebiasing current source for the diodes which is helpful in linearizing their performance particularly for low-level inputs and low operating temperatures. Expedients such as these have been useful in improving detector linearity but it still is difficult to achieve the degree of linearity required for some applications without undue detector circuit complexity and cost. Further, even if linearity error is adequately corrected in a detector circuit as originally manufactured, it generally is difficult to restore the same error limits upon subsequent replacement of any failed detector diodes, without factory adjustment or realignment.
The present invention has as its principal objective the provision of a video linear detector affording a high degree of linearity under all operating conditions, achieving such operation with little added circuit complexity and cost, and enabling the maintenance of linearity error within tolerances after component replacement.